1. Field of the Invention
The present invention relates to an electron source forming substrate, an electron source using the substrate, and an image display apparatus.
2. Related Background Art
Conventionally known electron-emitting devices are roughly divided into two types: thermal electron-emitting devices and cold-cathode electron-emitting devices. Examples of the cold-cathode electron-emitting devices include field emission type devices (hereinafter referred to as xe2x80x9cFE-typexe2x80x9d devices), metal/insulating-layer/metal-type devices (hereinafter referred to as xe2x80x9cMIM-typexe2x80x9d devices), and surface conduction electron-emitting devices.
Known examples of the FE-type devices are disclosed in W. P. Dyke and W. W. Dolan, xe2x80x9cField emission, Advance in Electron Physics, 8, 89 (1956)xe2x80x9d, C. A. Spindt, xe2x80x9cPhysical Properties of Thin-Film Field Emission Cathodes with Molybdenium Conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976), etc.
Examples of the surface conduction electron-emitting device are disclosed in M. I. Elinson, Recio Eng. Electron Phys., 10, 1290 (1965), etc.
A surface conduction electron-emitting device utilizes a phenomenon in which electron emission occurs by causing an electric current to flow through a small-area thin film formed on a substrate in parallel with the film surface. Reported examples of the surface conduction electron-emitting device include one using an SnO2thin film according to Elinson et al., one using an Au thin film [G. Dittmer: xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)], one using an In2O3/SnO2thin film [M. Hartwell and C. G. Fonstad: xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d 519(1975)], and one using a carbon thin film [Hisashi Araki, et al.: xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, page 22 (1983)].
To utilize an electron source, formed by arranging an electron-emitting device as mentioned above on a substrate, while holding it in an envelope in which a vacuum is maintained, it is necessary to join the electron source, the envelope and the other members to each other. This joining is generally effected through heating and fusion using frit glass. The typical heating temperature at this time is approximately 400 to 500xc2x0 C., and the typical heating time, which depends upon the size of the envelope, etc., is approximately 10 minutes to one hour.
It is desirable to use soda lime glass as the material of the envelope since it easily allows joint by frit glass and it is relatively inexpensive. A high strain point glass, in which Na is partly replaced with K to achieve a high strain point, is also preferable since it easily allows frit connection. Regarding the material of the substrate of the electron source, soda lime glass or high strain point glass is also preferable from the viewpoint of reliable joint with the envelope.
Soda lime glass contains a large amount of alkali metal, in particular, Na, which is in the form of Na2O. Na is subject to diffusion due to heat, so that when it is exposed to high temperature during processing, Na is diffused into various components formed on the soda lime glass, in particular, into the component constituting the electron-emitting device, thereby deteriorating its characteristics.
When a high strain point glass, described above, is used as the substrate of an electron source, the above-mentioned Na diffusion is mitigated since the Na content is small. However, it was found that Na diffusion also occurs in this case.
As a means for reducing the influence of Na, Japanese Patent Application Laid-Open No. 10-241550 and EP-A-850892 disclose an electron source forming substrate in which the Na concentration at least in the surface region on the side where the electron-emitting device is arranged is smaller as compared with that in the other regions, and an electron source forming substrate which includes a phosphorus containing layer.
However, it should be noted that an electron source forming substrate is usually formed of an insulating material, so that when driving is effected in a state in which a high voltage for causing electron emission is being applied, a charge-up phenomenon due to secondary electrons, etc. occurs in the exposed portion of the substrate. When nothing is done to cope with this charge-up phenomenon, it is difficult to perform driving in a stable manner for a long period of time, and the orbit of the electrons emitted from the electron source is disturbed, with the result that the electron emission characteristics undergo change with passage of time.
As an example of a means for reducing the influence of the charge-up phenomenon, U.S. Pat. No. 4,954,744 and Japanese Patent Application Laid-Open No. 8-180801 disclose a construction in which the substrate surface or the electron-emitting device surface are covered with an antistatic layer having a sheet resistance of 108 to 1010 xcexa9/xe2x96xa1.
It is an object of the present invention to provide an electron source forming substrate in which the change with passage of time of the electron emitting property of the electron-emitting device is reduced or in which it is possible to prevent charge-up from occurring on the substrate surface. Further, the present invention aims to provide an electron source and an image display apparatus using such a substrate.
In accordance with the present invention, there is provided an electron source forming substrate provided with an insulating material layer on a surface of a substrate, at which surface an electron-emitting device is disposed, wherein the insulating material layer has a plurality of partially exposed metal oxide particles on its surface.
In accordance with the present invention, there is further provided an electron source forming substrate provided with an insulating material layer on a surface of a substrate, at which surface an electron-emitting device is disposed, wherein the insulating material layer has a plurality of partially exposed metal oxide particles on its surface and a plurality of enclosed metal oxide particles.
In accordance with the present invention, there is further provided an electron source forming substrate provided with an SiO2 layer on a surface of the substrate, at which surface an electron-emitting device is disposed, wherein the SiO2 layer has a plurality of partially exposed metal oxide particles on its surface.
In accordance with the present invention, there is further provided an electron source forming substrate provided with an SiO2 layer on a surface of a substrate, at which surface an electron-emitting device is disposed, wherein the SiO2 layer has a plurality of partially exposed metal oxide particles on its surface, and a plurality of enclosed metal oxide particles.
In accordance with the present invention, there is further provided an electron source comprising a substrate and an electron-emitting device arranged on the substrate, wherein the substrate is one of the above-described electron source forming substrates.
In accordance with the present invention, there is further provided an image display apparatus comprising an envelope, an electron-emitting device arranged in the envelope, and an image display member adapted to display images through application of electrons from the electron-emitting device, wherein the substrate on which the electron-emitting device is arranged is one of the above-described electron source forming substrates.